John Siracusa, the Mac OS X guru who writes those insanely detailed and well-written Mac OS X reviews for Ars Technica, once told a story about the evolution of the HFS+ file system in Mac OS X - he said it was a struggle between the Mac guys who wanted the features found in BeOS' BFS, and the NEXT guys who didn't really like these features. In the end, the Mac guys won, and over the course of six years, Mac OS X reached feature parity - and a little more - with the BeOS (at the FS level).